In this type of cartridge, the thermostatic control is obtained using a thermostatic element expandable along an axis, on the one hand comprising a piston that is normally stationary relative to a hollow base of the cartridge, and on the other hand comprising a body rigidly connected to a control spool. This spool is movable along the axis inside the base of the cartridge so as to inversely vary the flow sections of the two fluids, called “hot fluid” and “cold fluid”, supplying the base through a first of its axial sides, in order to mix those fluids in variable proportions to obtain, downstream from the spool, a fluid, called “mixed fluid”, that flows along a heat-sensitive part of the thermostatic element and leaves the base through its second axial side. By modifying the position of the piston relative to the base, generally using an ad hoc adjusting mechanism, the thermostatic control temperature is set, i.e., the equilibrium temperature around which the temperature of the mixed fluid is controlled. This type of cartridge advantageously incorporates discs for controlling the flow rate of the cold and hot fluids sent toward the spool, those discs being arranged overhanging the first axial side of the basin and being supplied with the cold and hot fluids via flow channels extending from the second side to the first axial side of the base. It is even possible to have only one lever to control both these discs for controlling the flow rate and the aforementioned temperature adjusting mechanism: in that case, the thermostatic cartridge is described as single-control. WO-A-96/26475 provides one example of this.
In practice, the movements of the spool between two extreme positions, for which the flow of hot fluid is completely closed and the flow of cold fluid is completely closed, respectively, are approximately a millimeter, or even less, within standard-sized cartridges. As a result, the maximum flow rates of hot fluid and cold fluid that can be allowed into the base of those cartridges are limited. This limitation of the hot fluid and cold fluid flow rates is accentuated by the fact that the arrival of these fluids at the control spool is concentrated on limited respective portions of the outer periphery of the spool: in fact, the hot and cold fluids are respectively brought to the spool by having to cross through part of the base of the cartridge, while taking into account the more or less restrictive environment in which the base is to be installed. To bypass this difficulty, it is known, for example from the aforementioned document WO-A-96/26475, to hollow, within the base of the cartridge, peripheral grooves for distributing fluid around the spool, the hot fluid and cold fluid intakes respectively emerging in those grooves. However, in practice, this solution tends to reduce the inner diameter of the base in favor of its thickness to hollow the aforementioned grooves therein, which in particular limits the outer diameter of the spool and therefore limits the maximum fluid flow rates that can be controlled by that spool. Furthermore, this solution is expensive to implement, since manufacturing the base is complex: in the event the base is made by molding plastic material, the molding core necessarily has a large diameter to accommodate the presence of retractable pins that are necessary to mold the aforementioned grooves, as well as their junction with the hot fluid and cold fluid intakes.
One alternative to the solution disclosed in WO-A-96/26475 consists of inwardly providing the base with a distributor for the hot and cold fluids, making it possible to orient the fluid coming from the cold fluid inlet, the hot fluid inlet, respectively, toward the spool on its outer perimeter. The base can then be made using a less complex mold for injecting plastic material. However, due to the presence of the distributor, this design requires a larger number of pieces, as well as multiple seals to ensure tightness between those pieces. This solution leads to a more complicated assembly method, since a large number of pieces must be placed and tightness tests must be conducted to verify the presence and performance of the seals.